KYIV/MOSCOW (Reuters) -- Russian Prime Minister Vladimir Putin warned that Moscow would halt gas deliveries to Ukraine if payment were not received by March 7, and this could also affect supplies to Europe.

Ukraine is the main transit route for Russian gas exports to Europe, and a dispute over prices with Russia in January disrupted supplies to many countries at the height of winter.

Failure by Ukraine to pay, Putin said, could hurt transit flows to Europe.

"If as a result of law enforcement actions and arrests of a number of officials there will be no payment [for Russian gas deliveries], it will lead to the stoppage of our energy deliveries to our customers in Ukraine as well as customer in Europe," Putin said in Moscow on March 5.

He was speaking after Ukraine's SBU security service tried on March 5 to gain entry to the offices of the authority overseeing Ukraine's gas pipelines, but later left the building.

It was the second such incident in as many days and served to highlight worsening tension between Ukrainian President Viktor Yushchenko and Prime Minister Yulia Tymoshenko -- former allies now at loggerheads on nearly all issues.

Tymoshenko again denuounced the security forces action, accusing the president of dismanting Ukraine's legal bases.

On March 4, armed SBU officers burst into the offices of Ukraine's national energy company Naftogaz as part of investigations into what it said were abuses -- as the firm was making arrangements to settle a critical bill for Russian gas.

Naftogaz said it had paid 80 percent of the February gas bill to Russia and would settle the rest on March 5.

A spokeswoman for the Ukrtransgaz company that runs Ukraine's pipelines said a group of men in civilian clothes and apparently unarmed had demanded entry to the building. She said the group presented no documents or warrants.

A Naftogaz spokesman, Ilya Savin, said the group left the premises after about an hour after a standoff with members of parliament who had rushed to the scene.